For a base structure of a turnout for a permanent way, it is conventional to place wooden sleepers for the turnout in the track bed ballast at predetermined intervals and at right angles to the rail. Most sleepers used for the turnout are made of wood. Wooden sleepers are used because it is possible to place a base plate on the sleepers in the field, and to easily fix the base plate on the sleepers with track spikes or screw spikes by adjusting the position, then mount a rail on the base plate. Recently, sleepers made of synthetic resin or prestressed concrete are being used in place of the wooden sleepers.
Alternatively, a steel sleeper 21 having a cross section of substantially trapezoidal shape and a hollow inner space which opens at the bottom has been proposed, as shown in FIG. 12, wherein the inner space is filled with ballast to prevent the sleepers from subsiding, and both end faces of the sleeper in the longitudinal direction thereof are closed by press, thereby preventing the sleepers from moving in the direction of gauge, i.e., the so-called alignment deviation, by means of the ballast which fills the inner space of the sleeper.
The turnout comprises, as major components, a point section 22, a lead section 23, a crossing section 24 and a guard section 25, as shown in FIG. 13. In any one of these sections, rails 27 are mounted on the sleepers 26 with a positional relationship successively varying. Rails 27 and sleepers 26 are not at right angles with each other, and the crossing angle also is successively changing. The length of the sleeper also must be changed according to where it is positioned.
Thus, the turnout is very fragile because of its complicated structure compared to ordinary rail sections, and has shorter service life due to the use of wooden sleepers which tend to rot. More-over, sleepers used for a turnout generally are longer than the regular sleepers used in ordinary tracks, and, therefore, are more difficult to handle. Consequently, sleepers used for a turnout require more labor when being replaced.
Thus, it is very desirable to prevent damage or any other trouble from occurring to the sleepers to the utmost. However, a rail in a turnout has a radius of curvature which is generally smaller than in ordinary tracks, which causes a train running thereon to exert a sufficiently large lateral force that results in a displacement of the sleepers. As a result, it is necessary to frequently perform rail maintenance to correct the alignment deviation in order to prevent derailment accidents due to the alignment deviation.
In this respect, a conventional sleeper for a turnout provides a large resistive force to prevent the displacement in the longitudinal direction of the track by means of the ballast packed between the sleepers. However, with respect to the displacement in the direction perpendicular to the track, a conventional sleeper for a turnout provides a resistive force only with ballast built up on the track bed shoulder of both ends of the sleeper, which is not sufficient to prevent alignment deviation caused by a lateral force exerted on the track.
On the other hand, sleeper 21, as shown in FIG. 12, requires the ballast to be pressed toward the bottom of the sleeper by tamping the ballast from the side of the sleeper with a tie tamper in order to fill the inner space of the sleeper 21 with the ballast. This operation is very tedious and often results in insufficient packing of the ballast. Insufficient packing of the ballast leads to subsidence of the sleeper and poor resistance against a force exerted in the direction perpendicular to the track, which causes a displacement in said direction.
The present invention solves the problems of the above-described prior art, and an object of the present invention is to provide a base structure of a turnout which has high durability and is capable of reliably preventing lateral displacement.